I wanted to join in the conversation here as well. In the scenario presented, I personally saw very little wrong as presented. I think the primary issue here is the definition of "justice".
While attending the National Firearms Examiner Academy, the students had the pleasure of having an federal public defense attorney provide a several hour talk/lecture on courtroom testimony. The first topic we discussed was the concept of "justice". He started out by asking us "what is 'Justice'"? One of us fell into the trap by saying it's the truth.
He laughed. Justice is not about the truth, it's about "fairness" or following the rules of the legal system. One of the rules
is a requirement to tell the truth. Another rule (and perhaps a more important once, since it in the Bill of Rights) is the right of a defendant to not be forced self incriminate.
So what does this have to do with the presented scenario? Well, let's look at the purpose a expert hired by a defense attorney. This expert is providing a defendant an (re)examination of the evidence, and during that examination, the expert should be aware of his obligation to not violate the defendant's right of non-self incrimination. This obligation to Fifth Amendment can create some real ethical dilemmas (as has been outlined by Pete Barnet in past CACNews issues). Under this service, the Criminalist is not obligated to divulge incriminating evidence; in fact purposely doing so would likely be in violation of the defendant's rights.
This concept can be really foreign to many of us who spend our entire career working in law enforcement-based laboratories. In this function, we ARE obligated to divulge exculpatory information. Why? Because it's about fairness to the defendant, and ensure that he/she gets a FAIR trial (i.e. Justice).
I think we can all agree a defendant has the right to have evidence re-examined by his/her own expert. Right? If so, then that re-examination requires that the physical evidence consultant be aware of his/hers client's rights and to not violate those rights. Doing this is serving justice and I see no conflict between IV(D) and the Preamble.